Integrated circuit device having an injection-locked oscillator

ABSTRACT

A variable injection-strength injection-locked oscillator (ILO) is described. The variable injection-strength ILO can output an output clock signal based on an input clock signal. The variable injection-strength ILO can pause, restart, slow down, or speed up the output clock signal synchronously with respect to the input clock signal in response to receiving power mode information. Specifically, the variable injection-strength ILO can be operated under relatively strong injection when the input clock signal is paused, restarted, slowed down, or sped up.

RELATED APPLICATION

This application is a continuation of, and claims priority to, U.S. application Ser. No. 13/988,615, having the same title and inventors as the instant application, filed 21 May 2013, which is herein incorporated by reference in its entirety for all purposes. U.S. application Ser. No. 13/988,615 is a national stage application of, and claims priority to, International Application No. PCT/US11/60215, having the same title and inventors as the instant application, filed 10 Nov. 2011, which is herein incorporated by reference in its entirety for all purposes. International Application No. PCT/US11/60215 claims benefit of U.S. Provisional Application No. 61/419,459, having the same title and inventors as the instant application, filed 3 Dec. 2010, which is herein incorporated by reference in its entirety for all purposes.

FIELD

This disclosure relates to electronic circuits. More specifically, this disclosure generally relates to an injection-locked oscillator (ILO), for example, in an integrated circuit device.

BACKGROUND Related Art

The mobile computing revolution has enhanced the efficiency in how people communicate and interact with one another. Mobile devices are usually designed to meet stringent power constraints so that they can operate on batteries for a reasonably long time. To reduce power consumption, mobile devices may use circuits that have multiple power modes. Specifically, a mobile device may need to transition a circuit rapidly from one power mode to another power mode.

Some circuits may not be suitable for use in devices that have multiple power modes, especially if the circuits need to be transitioned rapidly from one power mode to another power mode. Further, in some circuits, latency may be incurred when recovering from power down modes. Specifically, powering up an ILO can create unpredictable transients in the ILO's output clock signal. Furthermore, latching and unlatching the ILO's output clock signal synchronously with respect to the input clock signal is not practical at high clock frequencies.

BRIEF DESCRIPTION OF THE FIGURES

FIG. 1 illustrates a variable injection-strength injection-locked oscillator in accordance with some embodiments described in this disclosure.

FIGS. 2A-2C illustrate signal waveforms associated with a variable injection-strength ILO operating in a weak-injection-strength mode in accordance with some embodiments described in this disclosure.

FIGS. 3A-3C illustrate signal waveforms associated with a variable injection-strength ILO operating in a strong-injection-strength mode in accordance with some embodiments described in this disclosure.

FIG. 4 illustrates a variable injection-strength ILO in accordance with some embodiments described in this disclosure.

FIG. 5 illustrates a variable injection-strength ILO in accordance with some embodiments described in this disclosure.

FIG. 6 illustrates a variable injection-strength ILO in accordance with some embodiments described in this disclosure.

FIG. 7A illustrates a variable injection-strength ILO that is capable of being powered down during a power saving mode in accordance with some embodiments described in this disclosure.

FIG. 7B illustrates waveforms associated with a variable injection-strength ILO that is capable of being powered down during a power saving mode in accordance with some embodiments described in this disclosure.

FIG. 8 illustrates a variable injection-strength ILO that includes a tank circuit (i.e., an oscillator based on an inductance/capacitance pair) in accordance with some embodiments described in this disclosure.

FIG. 9 illustrates a variable injection-strength ILO that includes a ring oscillator in accordance with some embodiments described in this disclosure.

FIG. 10 presents a flowchart that illustrates a process for operating a variable injection-strength ILO in accordance with some embodiments described in this disclosure.

FIG. 11 illustrates a memory controller that includes a variable injection-strength ILO in accordance with some embodiments described in this disclosure.

DETAILED DESCRIPTION

Embodiments presented in this disclosure are directed to methods and apparatuses featuring an injection-locked oscillator (ILO) whose injection strength can be varied based on power mode information. In this disclosure, unless otherwise stated, the phrase “based on” means “based solely or partly on.”

FIG. 1 illustrates a variable injection-strength ILO in accordance with some embodiments described in this disclosure. Variable injection-strength ILO 102 outputs output clock signal 104 based on input clock signal 106. In general, the methods and apparatuses described in this disclosure are applicable to any system that uses one or more ILOs.

An integrated circuit device, or circuits contained in such a device, can have multiple power modes. In some embodiments described in this disclosure, the integrated circuit device, or the circuits contained in the device, can transition rapidly from one power mode to another power mode. In a normal power mode, one or more parts of a circuit may be clocked using a clock signal that is operating at a normal clock frequency. In a power saving mode, the clock signal may be paused and/or the frequency of the clock signal may be substantially reduced in one or more parts of the circuit to reduce the dynamic power consumption of the circuit. Note that a circuit can have multiple power saving modes, e.g., different power saving modes of a circuit may slow down and/or pause the clock in different parts of the circuit.

Whenever a circuit transitions from one power mode to another, clock signals may need to be paused, slowed down, restarted, and/or sped up. In some embodiments, a circuit may be calibrated at system startup so that the data signal is sampled in the middle of the data eye. To operate correctly, the circuit may require the clock signal to be cleanly paused and restarted. Some embodiments provide a fast turn-on/turn-off apparatus that can be used to cleanly pause, restart, slow down, or speed up the clock signal.

According to one definition, when a clock signal is cleanly paused, restarted, slowed down, or sped up, the clock signal does not cause unpredictable changes to the circuit state. According to another definition, an output clock signal of an ILO is cleanly paused, restarted, slowed down, or sped up if the output clock signal synchronously tracks the input clock signal as the input clock signal is paused, restarted, slowed down, or sped up. According to one definition, an output clock signal synchronously tracks an input clock signal if each transition in the input clock signal corresponds to exactly one well-defined transition in the output clock signal. Note that these definitions are neither exhaustive nor mutually exclusive.

In an embodiment, the ILO can be based on a tank circuit (i.e., an inductor/capacitor oscillator) or a ring oscillator, with one or more nodes for receiving an input clock signal, and one or more nodes for outputting an output clock signal. In some embodiments, injection locking or injection pulling may occur when the oscillator is perturbed by an input clock signal whose frequency is relatively close to the oscillator's fundamental frequency, or relatively close to a sub-harmonic or a super-harmonic of the oscillator's fundamental frequency.

The behavior of an ILO, in embodiments described herein, may depend on the injection strength. If the injection strength is relatively weak, the oscillator runs relatively autonomously except that the oscillator's frequency and steady-state phase are dictated by the input clock signal once the ILO locks onto the input clock signal. In some embodiments described herein, ILOs are operated under relatively weak injection to remove clock jitter, to de-skew clock signals, and/or to generate clock signals.

In some embodiments, the ILO is operated under relatively strong injection so that the injection signal overcomes the natural oscillation of the ILO. When an ILO is operated under relatively strong injection by an embodiment, the ILO's output clock signal can pause, restart, slow down, and speed up synchronously with respect to the input clock signal when the input clock signal is paused, restarted, slowed down, and sped up, respectively. An embodiment may not operate the ILO under relatively strong injection when the benefits of operating the ILO under relatively weak injection are needed.

In some embodiments, when the circuit transitions from one power mode to another, variable injection-strength ILO 102 can be operated under relatively strong injection so that the output clock signal can be synchronously paused, restarted, slowed down, and/or sped up with respect to the input clock signal. Once the circuit has transitioned to the new power mode, the ILO may be operated under relatively weak injection. In some embodiments, the performance requirements may be such that the benefits of operating the ILO under relatively weak injection are not needed. In these embodiments, the ILO may continue to be operated under relatively strong injection even after the transition to the new power mode has been completed.

Specifically, variable injection-strength ILO 102 can receive power mode information 108, which may indicate that the circuit is transitioning from one power mode to another. For example, variable injection-strength ILO 102 may receive power mode information 108 that indicates that a circuit is about to enter a power saving mode. In response, variable injection-strength ILO 102 may increase the injection strength so that variable injection-strength ILO 102 operates under relatively strong injection. When variable injection-strength ILO 102 is operating under relatively strong injection, input clock signal 106 may pause or the clock frequency of input clock signal 106 may reduce substantially (e.g., halve). If input clock signal 106 pauses, output clock signal 104 may pause synchronously with respect to input clock signal 106. If the clock frequency of input clock signal 106 reduces substantially (e.g., halves), output clock signal 104 may synchronously track input clock signal 106, so that the clock frequency of output clock signal 104 also reduces accordingly.

Subsequently, input clock signal 106 may restart or the clock frequency of input clock signal 106 may increase substantially (e.g., double). If input clock signal 106 restarts, output clock signal 104 may restart synchronously with respect to input clock signal 106. If the clock frequency of input clock signal 106 increases substantially (e.g., doubles), output clock signal 104 may synchronously track input clock signal 106, so that the clock frequency of output clock signal 104 also increases accordingly. Variable injection-strength ILO 102 may then receive power mode information 108 that indicates that the circuit has completed transitioning to a power mode, e.g., a normal power mode. In response, variable injection-strength ILO 102 may decrease the injection strength so that the ILO operates under relatively weak injection.

In some embodiments, the ILO locks onto the input clock signal over a range of frequency values, called the ILO's locking range. In these embodiments, the locking range can be defined as the frequency range over which the output clock signal of the ILO synchronously tracks the input clock signal. According to one definition, the output clock signal synchronously tracks the input clock signal if the frequency of the output clock signal tracks the frequency of the input clock signal. In these embodiments, the phase delay between the output clock signal and the input clock signal may change when the frequency of the input clock signal is changed.

Increasing the injection strength can be viewed as increasing the locking range of variable injection-strength ILO 102. Conversely, decreasing the injection strength can be viewed as decreasing the locking range of variable injection-strength ILO 102.

Variable injection-strength ILO 102 can be viewed as having multiple operating modes, each with a different locking range. For example, variable injection-strength ILO 102 can have a first operating mode, e.g., a normal-locking-range mode, and a second operating mode, e.g., a large-locking-range mode. In the normal-locking-range mode, output clock signal 104 synchronously tracks input clock signal 106 over a normal frequency range, and in the large-locking-range mode, output clock signal 104 synchronously tracks input clock signal 106 over a large frequency range, which is greater than the normal frequency range.

The injection strength in the large-locking-range mode is greater than the injection strength in the normal-locking-range mode. Variable injection-strength ILO 102 can be operated in the normal-locking-range mode when the circuit is operating in a normal power mode. Variable injection-strength ILO 102 can be operated in the large-locking-range mode when the circuit transitions from one power mode to another, e.g., before the input clock signal is paused or slowed down in a power saving mode.

FIGS. 2A-2C illustrate signal waveforms associated with a variable injection-strength ILO operating in a weak-injection-strength mode in accordance with some embodiments described in this disclosure. The signal waveforms shown in FIGS. 2A-2C are for illustration purposes only. Input clock waveforms 202, 206, and 210 can correspond to input clock signal 106. Output clock waveforms 204, 208, and 212 can correspond to output clock signal 104. Output clock waveforms 204, 208, and 212 can have a phase delay with respect to input clock waveforms 202, 206, and 210, respectively. However, phase delays have not been shown in FIGS. 2A-2C for the sake of clarity and ease of discourse.

In a weak-injection-strength mode, a variable injection-strength ILO can substantially reduce jitter from the input clock signal. For example, as shown in FIG. 2A, the jitter in input clock waveform 202 has been removed in output clock waveform 204.

In a weak-injection-strength mode, if the input clock signal is paused, a variable injection-strength ILO may continue outputting an output clock signal whose frequency is approximately equal to the ILO's free-running frequency. For example, as shown in FIG. 2B, output clock waveform 208 toggles at the ILO's free-running frequency even when input clock waveform 206 is paused.

In a weak-injection-strength mode, a variable injection-strength ILO may not lock on the input clock signal if the frequency of the input clock signal is changed substantially. If the ILO does not lock on the input clock signal, it may output a clock signal whose frequency is equal to the ILO's free-running frequency. As shown in FIG. 2C, when the frequency of input clock waveform 210 changes from f to f/2, output clock waveform 212 may continue to output a clock signal at frequency f, although perhaps at a different phase (not shown in FIG. 2C).

FIGS. 3A-3C illustrate signal waveforms associated with a variable injection-strength ILO operating in a strong-injection-strength mode in accordance with some embodiments described in this disclosure. The signal waveforms shown in FIGS. 3A-3C are for illustration purposes only. Input clock waveforms 302, 306, and 310 can correspond to input clock signal 106. Output clock waveforms 304, 308, and 312 can correspond to output clock signal 104. Output clock waveforms 304, 308, and 312 can have a phase delay with respect to input clock waveforms 302, 306, and 310, respectively. However, phase delays have not been shown in FIGS. 3A-3C for the sake of clarity and ease of discourse.

In comparison to a weak-injection-strength mode, a variable injection-strength ILO operating in a strong-injection-strength mode may not be able to reduce as much jitter from the input clock signal over as wide a range of jitter frequencies. In other words, the variable injection-strength ILO may pass more high frequency jitter from the input clock waveform to the output clock waveform in a strong-injection-strength mode than in a weak-injection-strength mode. For example, as shown in FIG. 3A, the jitter in input clock waveform 302 has been reduced by a much lesser extent in output clock waveform 304.

In a strong-injection-strength mode, if the input clock signal pauses, a variable injection-strength ILO can pause the output clock signal synchronously with respect to the input clock signal. For example, as shown in FIG. 3B, output clock waveform 308 pauses synchronously with respect to input clock waveform 306.

In a strong-injection-strength mode, a variable injection-strength ILO may synchronously track the input clock signal even if the frequency of the input clock signal is changed substantially. For example, as shown in FIG. 3C, output clock waveform 312 synchronously tracks input clock waveform 310 as it changes its frequency from f to f/2.

FIG. 4 illustrates a variable injection-strength ILO in accordance with some embodiments described in this disclosure. Variable injection-strength ILO 402 is capable of varying the injection strength in response to receiving power mode information 408. Variable injection-strength ILO 402 can include amplifier 412, injection-strength controller 414, and ILO 410. Input clock signal 406 can be amplified by amplifier 412 to produce adjusted input clock signal 418. Adjusted input clock signal 418 can be provided as input to ILO 410, which can produce output clock signal 404. ILO 410 may receive free-run frequency control signal 416, which can be used to control the free-running frequency of an oscillator within ILO 410.

The gain of amplifier 412 can be controlled by injection-strength controller 414. Injection-strength controller 414 can increase the gain of amplifier 412 to operate ILO 410 under relatively strong injection, and decrease the gain of amplifier 412 to operate ILO 410 under relatively weak injection. For example, variable injection-strength ILO 402 may receive power mode information 408 that indicates that a circuit is about to transition between two power modes, e.g., from a normal power mode to a power saving mode. In response, injection-strength controller 414 may increase the gain of amplifier 412 so that ILO 410 operates under relatively strong injection. Subsequently, variable injection-strength ILO 402 may receive power mode information 408 that indicates that a circuit has completed transitioning to a power mode, e.g., a normal power mode. In response, injection-strength controller 414 may decrease the gain of amplifier 412 so that ILO 410 operates under relatively weak injection.

FIG. 5 illustrates a variable injection-strength ILO in accordance with some embodiments described in this disclosure. Variable injection-strength ILO 502 is capable of varying the injection strength in response to receiving power mode information 508. Variable injection-strength ILO 502 can include injection-strength controller 514 and ILO 510. Input clock signal 506 can be provided as input to ILO 510, which can produce output clock signal 504.

ILO 510 may receive free-run frequency control signal 516, which can be used to control the free-running frequency of an oscillation signal within ILO 510. The oscillation signal within ILO 510 can be perturbed based on input clock signal 506. The output from injection-strength controller 514 can be used to control the amplitude of the oscillation signal within ILO 510. Injection-strength controller 514 can decrease the amplitude of the oscillation signal within ILO 510 to operate ILO 510 under relatively strong injection, and increase the amplitude of the oscillation signal within ILO 510 to operate ILO 510 under relatively weak injection.

FIG. 6 illustrates a variable injection-strength ILO in accordance with some embodiments described in this disclosure. Variable injection-strength ILO 602 is capable of varying the injection strength in response to receiving power mode information 608. Variable injection-strength ILO 602 can include injection-strength controller 614 and ILO 610. Input clock signal 606 can be provided as input to injection clock signal generator 618, which may output multiple copies of input clock signal 606 which may or may not have different phase delays. The multiple outputs from injection clock signal generator 618 may be provided as inputs at multiple injection points in ILO 610, which can produce output clock signal 604.

ILO 610 may receive free-run frequency control signal 616, which can be used to control the free-running frequency of an oscillation signal within ILO 610. The output from injection-strength controller 614 can be used to control the number of injection points in ILO 610 that are injected with an injection clock signal. Injection-strength controller 614 can increase the number of injection points to operate ILO 610 under relatively strong injection, and decrease the number of injection points to operate ILO 610 under relatively weak injection.

FIG. 7A illustrates a variable injection-strength ILO that is capable of being powered down during a power saving mode in accordance with some embodiments described in this disclosure. Variable injection-strength ILO 702 outputs output clock signal 704 based on input clock signal 706. Variable injection-strength ILO 702 can receive power mode information 708 and power down/up information 710 (e.g., an enable/disable signal).

Latch 712 receives output clock signal 704 and produces latch output 714. When latch 712 is unlatched, it passes the input signal to its output, i.e., latch output 714 toggles synchronously with output clock signal 704. When latch 712 is latched, latch output 714 outputs the latched signal value. Latch 712 can be latched and unlatched based on power down/up information 710. When input clock signal 706 is toggling (e.g., in a normal power mode or a slow down mode), latch 712 is kept unlatched. Latch 712 may be latched after input clock signal 706 has been paused.

FIG. 7B illustrates waveforms associated with the system shown in FIG. 7A in accordance with some embodiments described in this disclosure. The waveforms shown in FIG. 7B are for illustration purposes only. As shown in FIG. 7B, variable injection-strength ILO 702 may receive power mode information 708 that indicates that a circuit is about to transition between two power modes, e.g., from a normal power mode to a power saving mode. In response, variable injection-strength ILO 702 may increase the injection strength so that the ILO operates under relatively strong injection. After power mode information 708 is received by variable injection-strength ILO 702, input clock signal 706 may pause. Since variable injection-strength ILO 702 is operating under relatively strong injection, output clock signal 704 pauses synchronously with respect to input clock signal 706. Next, power down/up information 710 may indicate that variable injection-strength ILO 702 is to be powered down. In response, the signal value of output clock signal 704 may be latched by latch 712, and then variable injection-strength ILO 702 may be powered down.

Subsequently, power down/up information 710 may indicate that variable injection-strength ILO 702 is to be powered up. In response, variable injection-strength ILO 702 may be powered up, and then latch 712 may be unlatched after the output of variable injection-strength ILO 702 has stabilized.

Next, input clock signal 706 may restart. Since variable injection-strength ILO 702 is operating under relatively strong injection, it restarts output clock signal 704 synchronously with respect to input clock signal 706. Further, since latch 712 is unlatched, latch output 714 outputs the output clock signal 704, which was restarted synchronously with respect to input clock signal 706. Variable injection-strength ILO 702 may then receive power mode information 708 that indicates that the circuit has entered a normal power mode. In response, variable injection-strength ILO 702 may decrease the injection strength so that the ILO operates under weak injection.

FIG. 8 illustrates a variable injection-strength ILO that includes a tank circuit (i.e., an oscillator based on an inductance/capacitance pair) in accordance with some embodiments described in this disclosure. Signals S_(INJ) and S _(INJ) correspond to the injection clock signal, signals S_(OUT) and S _(OUT) correspond to the output clock signal, and V_(DD) is the supply voltage. The amplitude of the ILO's oscillation signal can be changed by using bias signal S_(BIAS). Specifically, the ILO can be operated under relatively strong injection by either increasing S_(BIAS,INJ) (which, in turn, increases the amplitude of the injection clock signal) or by decreasing S_(BIAS) (which, in turn, decreases the amplitude of the oscillator's signal). Conversely, the ILO can be operated under relatively weak injection by either decreasing S_(BIAS,INJ) (which, in turn, decreases the amplitude of the injection clock signal) or by increasing S_(BIAS) (which, in turn, increases the amplitude of the oscillator's signal). The free-running frequency of the LC oscillator can be changed by using the variable capacitor.

FIG. 9 illustrates a variable injection-strength ILO that includes an inverter based ring oscillator in accordance with some embodiments described in this disclosure. Signal S_(OUT) can correspond to the output clock signal and signals S_(INJ,1) and S_(INJ,S2) can correspond to the injection clock signals that are injected at two different injection points. Note that the injection clock signals that are injected at the two injection points may have different phases. The ILO can be operated under relatively strong injection by injecting the injection clock signal at both injection points. The ILO can be operated under relatively weak injection by injecting the injection clock signal at only one of the two injection points. The ILO can be operated under relatively strong injection by injecting the injection clock signal at one or both injection points with a relatively low impedance (or high current) compared to the inverter device impedances (or currents). The ILO can be operated under relatively weak injection by injecting the injection clock signal at one or both injection points with a relatively high impedance (or low current) compared to the inverter device impedances (or currents). The ILO can be operated under relatively strong injection by increasing the impedance (or decreasing the drive current) of the inverters relative to the impedance (or drive current) of the injection signals. The ILO inverters can be tri-state inverters which have a high output impedance state, and the inverters can be configured into the high output impedance state to operate the ILO under relatively strong injection or into the normal impedance state to operate the ILO under relatively weak injection.

FIG. 10 presents a flowchart that illustrates a process for operating a variable injection-strength ILO in accordance with some embodiments described in this disclosure. A variable injection-strength ILO may receive power mode information (operation 1002). In response to receiving the power mode information, the variable injection-strength ILO can change the injection strength. Specifically, the variable injection-strength ILO can increase injection strength if the power mode information indicates that a circuit is about to transition between two power modes (operation 1004). The variable injection-strength ILO can optionally decrease injection strength if the power mode information indicates that a circuit has completed transitioning to a power mode (operation 1006). Specifically, if the performance requirements are such that the benefits of operating the ILO under relatively weak injection are not needed, then the ILO may continue to be operated under relatively strong injection even after the transition to the power mode has been completed.

FIG. 11 illustrates a memory controller that includes a variable injection-strength ILO in accordance with some embodiments described in this disclosure.

Memory controller 1100 may be coupled with memory module 1104 via one or more signal lines, which may carry control signals, clock signals, and/or data signals. Memory controller 1100 may receive power mode information 1108, and include one or more ILOs, such as, variable injection-strength ILO 1102. In some embodiments, memory controller 1100 may use variable injection-strength ILO 1102 to remove clock jitter, to de-skew clock signals, and/or to generate clock signals. In some embodiments, memory controller 1100 may change the injection strength of variable injection strength ILO 1102 based on power mode information 1108.

Any data structures and/or code described in this disclosure can be stored on a computer-readable storage medium, which may be any device or medium that can store code and/or data for use by a computer system. The computer-readable storage medium includes, but is not limited to, volatile memory, non-volatile memory, magnetic and optical storage devices such as disk drives, magnetic tape, CDs (compact discs), DVDs (digital versatile discs or digital video discs), or other media capable of storing computer-readable media now known or later developed.

The methods and/or processes described in this disclosure can be embodied as code and/or data, which can be stored in a computer-readable storage medium as described above. When a computer system reads and executes the code and/or data stored on the computer-readable storage medium, the computer system performs the methods and/or processes.

Furthermore, the methods and/or processes described in this disclosure can be embodied in hardware. Hardware embodiments include, but are not limited to, application-specific integrated circuit (ASIC) chips, field-programmable gate arrays (FPGAs), and other programmable-logic devices now known or later developed.

Various modifications to the disclosed embodiments will be readily apparent to those skilled in the art, and the general principles defined herein may be applied to other embodiments and applications without departing from the spirit and scope of the present disclosure. Thus, the scope of the present disclosure is not limited to the embodiments shown, but is to be accorded the widest scope consistent with the principles and features disclosed herein. 

What is claimed is:
 1. A circuit, comprising: an input to receive an input clock signal; an output to output an output clock signal; and a variable injection-strength injection-locked oscillator (ILO), wherein the variable injection-strength ILO generates the output clock signal based on the input clock signal and power mode information, and wherein, while the variable injection-strength ILO is in a powered on state, the variable injection-strength ILO is capable of synchronously pausing the output clock signal with respect to the input clock signal when the input clock signal pauses.
 2. The circuit of claim 1, wherein the variable injection-strength ILO operates in one of multiple operating modes based on the power mode information; wherein, in a first operating mode, the output clock signal is not capable of pausing synchronously with respect to the input clock signal when the input clock signal pauses; and wherein, in a second operating mode, the output clock signal is capable of pausing synchronously with respect to the input clock signal when the input clock signal pauses.
 3. The circuit of claim 2, wherein the variable injection-strength ILO generates an adjusted input signal based on the input signal, wherein the adjusted input signal is used as an injection signal in the variable injection-strength ILO, and wherein the amplitude of the adjusted input clock signal in the second operating mode is greater than the amplitude of the adjusted input clock signal in the first operating mode.
 4. The circuit of claim 2, wherein an oscillation signal within the variable injection-strength ILO is perturbed based on the input clock signal, and wherein the amplitude of the oscillation signal in the second operating mode is less than the amplitude of the oscillation signal in the first operating mode.
 5. The circuit of claim 2, wherein the input clock signal is injected at multiple injection points in the variable injection-strength ILO, and wherein the number of injection points in the second operating mode is greater than the number of injection points in the first operating mode.
 6. The circuit of claim 2, further comprising control circuitry to operate the variable injection-strength ILO in the second operating mode or the first operating mode based on the power mode information.
 7. The circuit of claim 6, wherein the control circuitry operates the variable injection-strength ILO in the second operating mode if the power mode information indicates that the circuit is about to transition between two power modes.
 8. The circuit of claim 6, wherein the control circuitry operates the variable injection-strength ILO in the first operating mode if the power mode information indicates that the circuit has completed transitioning to a power mode.
 9. The circuit of claim 6, wherein the control circuitry latches the output clock signal and powers down the variable injection-strength ILO after the output clock signal pauses synchronously with respect to the input clock signal.
 10. The circuit of claim 9, wherein the circuitry powers up the variable injection-strength ILO and unlatches the output clock signal before the input clock signal is restarted.
 11. A circuit, comprising: an input to receive an input clock signal; an output to output an output clock signal; a variable injection-strength injection-locked oscillator (ILO), wherein the variable injection-strength ILO generates the output clock signal based on the input clock signal, wherein the variable injection-strength ILO has multiple operating modes including a first operating mode and a second operating mode, wherein the locking range of the variable injection-strength ILO in the first operating mode is less than the locking range of the variable injection-strength ILO in the second operating mode; and control circuitry to switch the variable injection-strength ILO from the first operating mode to the second operating mode before circuitry clocked by the output clock signal transitions from a high power mode to a low power mode.
 12. The circuit of claim 11, wherein the control circuitry continues to operate the variable injection-strength ILO in the second operating mode while the circuitry clocked by the output clock signal remains in the low power mode.
 13. The circuit of claim 11, wherein the control circuitry switches the variable injection-strength ILO from the second operating mode to the first operating mode after the circuitry clocked by the output clock signal has completed transitioning back from the low power mode to the high power mode.
 14. The circuit of claim 11, wherein the variable injection-strength ILO generates an adjusted input clock signal based on the input clock signal, wherein the adjusted input clock signal is used as an injection clock signal in the variable injection-strength ILO, and wherein the amplitude of the adjusted input clock signal in the second operating mode is greater than the amplitude of the adjusted input clock signal in the first operating mode.
 15. The circuit of claim 11, wherein an oscillation signal within the variable injection-strength ILO is perturbed based on the input clock signal, and wherein the amplitude of the oscillation signal in the second operating mode is less than the amplitude of the oscillation signal in the first operating mode.
 16. The circuit of claim 11, wherein the input clock signal is injected at multiple injection points in the variable injection-strength ILO, and wherein the number of injection points in the second operating mode is greater than the number of injection points in the first operating mode.
 17. A circuit, comprising: an input to receive an input clock signal; an output to output an output clock signal; a variable injection-strength injection-locked oscillator (ILO), wherein the variable injection-strength ILO generates an output clock signal based on an input clock signal, wherein the multiple operating modes include a first operating mode and a second operating mode; wherein, in the first operating mode, the variable injection-strength ILO is capable of synchronously tracking the input clock signal over a first frequency range; wherein, in the second operating mode, the variable injection-strength ILO is capable of synchronously tracking the input clock signal over a second frequency range, wherein the second frequency range is greater than the first frequency range; and control circuitry to switch the variable injection-strength ILO from the first operating mode to the second operating mode before circuitry clocked by the output clock signal transitions from a high power mode to a low power mode.
 18. The circuit of claim 17, wherein the control circuitry continues to operate the variable injection-strength ILO in the second operating mode while the circuitry clocked by the output clock signal remains in the low power mode.
 19. The circuit of claim 17, wherein the control circuitry switches the variable injection-strength ILO from the second operating mode to the first operating mode after the circuitry clocked by the output clock signal has completed transitioning back from the low power mode to the high power mode.
 20. The circuit of claim 17, wherein the variable injection-strength ILO generates an adjusted input clock signal based on the input clock signal, wherein the adjusted input clock signal is used as an injection signal in the variable injection-strength ILO, and wherein the amplitude of the adjusted input clock signal in the second operating mode is greater than the amplitude of the adjusted input clock signal in the first operating mode. 